1. Field of the Invention
The present invention generally relates to the art of microfabrication of semiconductor devices, more particularly, to a negative resist composition that can be developed with a basic aqueous solution without causing swelling, a method for forming a fine resist pattern thereof and a method for fabricating a semiconductor device. According to the present invention, a resist material having a lower absorbance and a high sensitivity for shorter wavelength radiation and high dry etching resistance can be provided. Thus, a semiconductor integrated circuit such as VLSI and ULSI etc., as well as other devices needing microfabrication such as a magnetic resistive head, and the like, can be advantageously fabricated.
2. Description of the Related Art
A photolithography technique using krypton fluoride excimer laser (wavelength: 248 nm, as referred to KrF hereinafter) has been dominating for mass production of highly miniaturized semiconductor devices due to availability of chemical amplification type resist such as the one proposed by H. Ito, et al. For example, reference should be made to J. M. J. Frechet et al., Proc Microcircuit Eng., 260 (1982), H. Ito et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86 (1983), H. Ito et al., “Polymers in Electronics”, ACS Symposium Series 242, and T. Davidson et al., ACS, 11 (1984), U.S. Pat. No. 4,491,628 (1985).
Recently, in relation to fabrication of a higher integrated circuit devices such as Gbit DRAMs, a lithography technique using ArF (Argon fluoride) excimer laser (wavelength: 193 nm) has been actively studied, wherein the ArF excimer laser emits a shorter wavelength radiation as compared with the KrF excimer laser. Since conventional phenol resins have a strong optical absorbance at such shorter wavelengths, the resin material constituting the base of the resist has to be changed. Thus, there is an urgent need of developing a resist material applicable for such shorter wavelength radiations.
As a chemical amplification type resist applicable for the wavelength of ArF radiation, positive resists have been actively studied (see, for example, K. Nozaki et al., Chem. Mater., 6, 1492 (1994), K. Nakano et al., Proc. SPIE, 2195, 194 (1994), R. D. Allen et al., Proc. SPIE, 2438, 474 (1994), Japanese Laid-Open patent application No.9-90637, K. Nozaki et al., Jpn. J. Appl. Phys., 35, L528 (1996), and K. Nozaki et al., J. Photopolym. Sci. Technol., 10(4), 545–550 (1997)).
However, there are few reports about single layer negative chemical amplification type resists. Most of the resists are cross-linking type resists.
For example, as described in A. Katsuyama et al., Abstracted Papers of Third International Symposium on 193 nm Lithography, 51 (1997), or in Maeda et al., Abstracts of the 58th Japan Society of Applied Physics No.2, 647 (3a-Sc-17) (1997), or in T. Naito et al., Proc. SPIE, 3333, 503 (1998), Japanese Laid-Open patent application No.2000-122288, or in Japanese Laid-Open patent application No.2000-147769, a cross-linking type resist is utilized for patterning, there is a report of cross-linking type resist in which there is caused a difference of solubility to a developer between an exposed area and an unexposed area by increasing the molecular weight as a result of cross-linking reaction at the exposed area. However, such an approach cannot avoid the problem of swelling of the exposed patterns, and the use thereof in the art of microfabrication of semiconductor devices is rather limited.
Recently, there is a report of a single-layer negative chemical amplification type resist that uses a polarity change, which in turn is caused by an intra-molecular lactonization that uses a hydroxycarboxylic acid structure (for example, reference should be made to Y. Yokoyama et al., J. Photopolym. Sci. Technol., 13(4), 579 (2000)). Further, there is a report of a single-layer negative chemical amplification resist that uses a pinacol rearrangement (for example, reference should be made to S. Cho et al., Proc. SPIE, 3999, 62 (2000)).
However, in the case of using the intra-molecular lactonization, there is a problem in that proportion of the polarity change is relatively small and it is difficult to perform patterning with high contrast. Also, in the case of the pinacol rearrangement, there are problems such as adhesion property to a substrate due to the inclusion of fluorine and preservation stability caused as a result of inclusion of maleic anhydride.
Thus, the resist utilizing pinacol arrangement has not been established. Although the inventors previously developed a single-layer negative chemical amplification type resist using polarity change that uses an inter-molecular protection reaction (Japanese Laid-Open patent application No.11-311860 and No.11-305436), there was a problem that no enough reactivity was achieved because of the fact that the reaction is an inter-molecular reaction.
A negative resist can be advantageously used when it is difficult to produce a mask with a positive resist or when the exposed area is small as in the case of the gate of a transistor, due to the fact that the unexposed area of the resist is dissolved. Further, the use of such a negative resist is advantageous also in the case of forming a phase shift mask used in the-technology of super-resolution exposure for obtaining a resolution equal to or less than the wavelength used for the exposure, and also in the Levenson mask, which is used for enhancing optical images.
Thus, a negative resist is hoped for also in the art of ArF exposure. These masks formed of the negative resist are considered also as being applicable to the case in which the resolution of equal to or less than 130 nm is required in combination with the use of ArF excimer radiation source. Thus, there is an urgent demand for a resist capable of resolving such a fine pattern without causing swelling.
Meanwhile, with increase of integration density of semiconductor devices, the number of interconnection layers is increasing also in addition to the miniaturization of the line width. In relation to such a demand, the requirement imposed to a resist material for lithographic process is becoming stringent every year. In addition to the resolution, the dimensional accuracy after etching has emerged recently as an important factor of a resist material. With the shifting of the exposure wavelength to a shorter side, it is expected that there appear difficulty in keeping up a sufficient transparency for the resist material. Thus, it is expected that the thickness of the resist layer becomes thin in such a future resist material. When the thickness of the resist layer is thus reduced, the etching property of the resist layer becomes a paramount problem in the fabrication process of miniaturized semiconductor devices. Similar problems appear also in the case of fabricating any highly miniaturized devices that use a highly miniaturized photolithographic patterning process such as the fabrication process of magneto-resistive heads for use in high-density magnetic recording.
Meanwhile, there is a proposal of surface imaging technique as an effective technology solving the foregoing problems. Particularly, there is a proposal of bilayer resist process that uses a resist composition containing silicon. The bilayer method comprises the steps of forming a lower resist layer by applying a solution containing an organic resin with a thickness of about 0.5 μm, followed by formation of an upper resist layer on the lower resist layer thus formed, with a thickness of about 0.1 μm. Next, the upper resist layer is patterned by an exposure and developing process to form a upper resist pattern, and the lower resist layer is subjected to an etching process by using the upper resist pattern as a mask. According to such a process, it becomes possible to form a resist pattern having a high aspect ratio.
The resist material for use in such a bilayer method is required to satisfy various requirements such as excellent exposure resolution, excellent storage stability, capability of being developed by basic aqueous solutions (alkaline developability), in other words, in addition to excellent resistance to oxygen reactive etching (hereinafter referred to as O2-RIE). At the present stage, however, there is no commercially available resist material that satisfies all of the above requirements.